Amorphous Selenium Avalanche Detector with Cascaded Lateral Design
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional solid-state radiation imaging detectors, such as silicon photomultipliers, face issues with poor photon detection efficiency, high cost, poor uniformity, and low yield due to stochastic avalanche gain and high electric field fluctuations, while amorphous selenium detectors struggle with charge trapping and manufacturing challenges in achieving high electric fields for improved imaging performance.
Innovation Solution
A field-shaping multi-well avalanche detector structure using an amorphous selenium photoconductive layer with a cascaded lateral design, featuring a high voltage source and collector regions, and a series of grids to localize the high-field avalanche region and prevent field hot-spots, allowing for stable and repeatable avalanche gain without increasing vertical thickness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If high electric field is applied to improve conversion gain in a-Se detectors, then detection efficiency improves, but charge trapping and manufacturing reliability deteriorate
Solution Approach 1:
The detector is divided into two distinct functional regions: a low-field absorption region (0-10 V/micron) where photons are converted to electron-hole pairs, and a high-field avalanche region (>30 V/micron) where charge multiplication occurs. This segmentation allows each region to operate at optimal field strength without compromising the other, resolving the contradiction between detection efficiency and manufacturing reliability.
Solution Approach 2:
Different electric field strengths are applied to different spatial locations within the detector. The absorption region maintains low electric field to prevent charge trapping and ensure uniform charge generation, while the avalanche region applies high electric field locally only where needed for charge multiplication, achieving high detection efficiency without compromising overall device reliability.
2Power
If vertical thickness is increased to achieve higher gain, then avalanche multiplication improves, but device complexity and manufacturing difficulty increase
Solution Approach 1:
The patent transitions from a vertical stack configuration to a lateral/cascaded configuration where multiple avalanche stages are arranged horizontally. This dimensional change allows achieving high cumulative gain through series connection of multiple low-gain stages without increasing vertical thickness, thereby reducing device complexity and manufacturing difficulty while maintaining high avalanche gain capability.
3Power
If conventional silicon photomultipliers are used to achieve high gain, then avalanche gain is achieved, but photon detection efficiency and uniformity deteriorate due to stochastic avalanche process
Solution Approach 1:
The patent changes the material parameter from silicon to amorphous selenium, which fundamentally alters the avalanche process characteristics. a-Se exhibits deterministic avalanche multiplication with very low excess noise factor (k≈0.01) compared to silicon, enabling high gain while maintaining excellent photon detection efficiency and uniformity. This material parameter change resolves the contradiction between achieving high avalanche gain and maintaining measurement precision.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration enhances signal rise time and gain levels, reduces charge injection, and achieves nearly ideal unipolar time-differential charge sensing with improved temporal resolution and detection efficiency, overcoming the limitations of existing technologies.
Implementation Method 1
a key feature of this impact ionization process is that only holes become hot carriers and undergo avalanche multiplication
Implementation Method 2
avalanche selenium devices are linear-mode devices with a very low k value
Implementation Method 3
the energy required to generate an electron-hole pair in a-Se is 50 eV at 10 V/micron
Implementation Method 4
a-Se has ̃90% detection efficiency in the blue wavelength which makes it ideal to be coupled to blue-emitting scintillators
Data Source
AI summary
Provided is a field shaping multi-well photomultiplier and method for fabrication thereof. The photomultiplier includes a field-shaping multi-well avalanche detector, including a lower insulator, an a-Se photoconductive layer and an upper insulator. The a-Se photoconductive layer is positioned between the lower insulator and the upper insulator. A light interaction region, an avalanche region, and a collection region are provided along a length of the photomultiplier, and the light interaction region and the collection region are positioned on opposite sides of the avalanche region.